Summary: public
RCTImagePicker (aka ImagePickerIOS) was previously displaying UI from a random thread, which is unsafe. This diff forces it to execute on the main thread instead.
Reviewed By: jspahrsummers
Differential Revision: D2657465
fb-gh-sync-id: 3c0fa6935061ccaa3e6ce649b4e3e8ad8c701384